The overall goals of this research are to elucidate the molecular mechanisms of the intercellular processes that occur during liver regeneration and tissue repair. Ultimately, we would like to know how these processes are involved in localizing the different liver cell types in the final precise tissue architecture that is required in a functional liver. Additionally, we would like to know if these processes are directly involved in regulating cell proliferation during regeneration and repair. The approach will be to study in vitro the readhesion of cells derived from quiescent and from regenerating rat liver. In previous studies, we examined the adhesive specificity of hepatocytes derived from quiescent rat liver and defined some of the conditions for the readhesion of these cells. We also succeeded in isolating a protein matrix from rat liver plasma membranes which may be involved in the adhesion process. In the proposed studies, we will further define the mechanism by which these cells readhere by examining the effects on adhesion of inhibitors and reagents which disrupt various cellular processes. We will determine whether magnesium and calcium ions affect hepatocyte adhesion by acting at an intracellular or extracellular location. These latter studies may also provide useful information on the effects on liver of hypercalcemia and hypomagnesemia, conditions which occur in a number of diseases. In our studies on the regenerating liver, we will measure the adhesive specificity of hepatocytes and sinusoidal cells (Kupffer cells and endothelial cells) derived from the regenerating tissue. Are these cells able specifically to recognize and adhere only to other cells with which they are normally in contact in vivo? Using different assays, we will measure the rates of cell-cell adhesion and attempt to isolate from the liver molecules that affect this adhesive rate. We will then determine if these molecules are the same as those involved in the actual adhesion reaction. With the isolation of these molecules and the elucidation of the molecular mechanism of the in vitro adhesion process, we can begin to make specific probes (such as antibodies) for the adhesive molecules and find specific inhibitors of the adhesion reaction. These tools will eventually be used to examine the physiological role of the "adhesion" molecules in vivo.